Field of the Invention
The present invention relates to an automatic focusing apparatus, e.g., a camera, and a control method therefor.
Description of the Related Art
Conventionally, an automatic focusing apparatus of an auto-focusing (AF) system which focuses on an object by moving a focus lens position according to a luminance signal obtained from an image sensor, such as a charge-coupled device (CCD), has been used in an electronic still camera or the like. In the automatic focusing apparatus, a focus evaluation value indicating a contrast within an AF area is calculated by integrating high-frequency components of a signal in the AF area set within an image plane. Then, a focus detection operation for acquiring a focus evaluation value for each position of a focus lens is performed by shifting the focus lens, to detect a position of the focus lens enabling the highest focus evaluation value, which is regarded as an in-focus point. Further, in an automatic focusing apparatus of the AF system, by repeatedly performing the focus detection operation, focusing can be also achieved on a moving object by tracking it.
As a technology relating to an automatic focusing apparatus which also enables focusing with respect to a moving object by tracking it, Japanese Patent Application Laid-Open No. 2004-212556, and Japanese Patent Application Laid-Open No. 2007-206433 are known. Japanese Patent Application Laid-Open No. 2004-212556 discusses an imaging apparatus equipped with an automatic focusing apparatus which causes an AF tracking to an object to be performed by repeating a focus detection operation by a lens movement before shooting. Further, Japanese Patent Application Laid-Open No. 2007-206433 discusses a technology for storing in advance in-focus positions after having performed the focus detection operation for each shooting, in a continuous shooting or the like, predicting an in-focus position before a next shooting based on the previous in-focus positions previously stored, thus determining a range for a focus detection operation.
However, in the above-described conventional technology, even in a case where a distance between an automatic focusing apparatus and an object has not changed, e.g., the object comes to rest, a focus detection operation is continuously performed so that the focus lens is sequentially moved. For this reason, a focus fluctuation always occurs, and a tracking ability to the object may deteriorate. In particular, in an electronic viewfinder (EVF) display using consecutive captured images, or the like, frames which are out-of focus may be generated, and accordingly visual quality may degrade. Further, the focus lens is sequentially moved, thus leading to an increase in battery consumption.